The Italian journalist kidnapped in Iraq arrived back in Rome yesterday as fury and confusion grew over the circumstances in which she was shot and one of her rescuers was killed by American soldiers.

The shooting in Iraq on Friday evening, which occurred as Giuliana Sgrena was being driven to freedom after being released by her captors, was fuelling anti-war activists in Italy and putting pressure on Prime Minister Silvio Berlusconi.

'The hardest moment was when I saw the person who had saved me die in my arms,' she said. Her poignant words and weak, haggard appearance as she had to be helped from the jet that brought her back from Baghdad are fuelling national rage.

Berlusconi, a staunch ally of the US who defied widespread public opposition to the Iraq war and sent 3,000 troops, took the rare step of summoning US ambassador Mel Sembler to his office.

He demanded that the US 'leave no stone unturned' in investigating the incident. President George Bush called Berlusconi to promise a full investigation.

Sgrena, 56, a journalist for the Communist newspaper Il Manifesto, was hit in the shoulder when US soldiers opened fire on the car she was travelling in as it approached a checkpoint less than a mile from Baghdad airport. The Italian secret service officer who had negotiated her release was killed as he shielded her from the gunfire. Two of his colleagues were also hurt.

Berlusconi prides himself on his close personal friendship with President George Bush, but he was grim-faced when he told reporters that someone would have to take responsibility 'for such a grave incident'.

The US Army claimed the Italians' vehicle had been seen as a threat because it was travelling at speed and failed to stop at the checkpoint despite warning shots being fired by the soldiers. A State Department official in Washington said the Italians had failed to inform the military of Sgrena's release.

Italian reconstruction of the incident is significantly different. Sgrena told colleagues the vehicle was not travelling fast and had already passed several checkpoints on its way to the airport. The Americans shone a flashlight at the car and then fired between 300 and 400 bullets at if from an armoured vehicle. Rather than calling immediately for assistance for the wounded Italians, the soldiers' first move was to confiscate their weapons and mobile phones and they were prevented from resuming contact with Rome for more than an hour.

Enzo Bianco, the opposition head of the parliamentary committee that oversees Italy's secret services, described the American account as unbelievable. 'They talk of a car travelling at high speed, and that is not possible because there was heavy rain in Baghdad and you can't travel at speed on that road,' Bianco said. 'They speak of an order to stop, but we're not sure that happened.'

Pier Scolari, Sgrena's partner who flew to Baghdad to collect her, put an even more sinister construction on the events, suggesting in a television interview that Sgrena was the victim of a deliberate ambush. 'Giuliana may have received information which led to the soldiers not wanting her to leave Iraq alive,' he claimed.

Sgrena was kidnapped on 4 February as she interviewed refugees from Falluja near a Baghdad mosque. Two weeks later her captors issued a video of her weeping and pleading for help, calling on all foreigners to leave Iraq. Italian journalists were subsequently withdrawn from the city after intelligence warnings of a heightened threat to their safety.

Italian newspapers reported yesterday that Sgrena had been in the hands of former Saddam loyalists and criminals, and that a ransom of between £4 million and £5 million had been paid for her release. The military intelligence officer who lost his life, Nicola Calipari, 51, was hailed as a national hero.